120
правок
Изменения
→permutations
==subsequences==
==permutations==
permutations :: List a -> List (List a)
permutations Nil = Nil
permutations (Cons x Nil) = (Cons (Cons x Nil) Nil)
permutations (Cons x xs) = insertAtEveryPosForList (permutations xs) x
where
insertAtEveryPos :: List a -> a -> Nat -> List (List a)
insertAtEveryPos str elem Zero = Cons (insert Zero elem Nil str) Nil
insertAtEveryPos str elem pos = (insertAtEveryPos str elem (pos -. natOne)) ++ (Cons (insert pos elem Nil str) Nil)
insertAtEveryPosForList :: List (List a) -> a -> List (List a)
insertAtEveryPosForList (Cons x Nil) elem = insertAtEveryPos x elem (length x)
insertAtEveryPosForList (Cons x xs) elem = (insertAtEveryPosForList xs elem) ++ (insertAtEveryPos x elem (length x))
==А так же==
* Дают тип какого-нибудь foldr и просят написать какой-нибудь foldr.
